#!/bin/dash

max=$(cat /sys/class/backlight/intel_backlight/max_brightness)
cur=$(cat /sys/class/backlight/intel_backlight/brightness)
step=$(($max*$1/100))
if [ $(($cur+$step)) -lt 0 ]; then
    setbrt 0
    exit 1
fi
if [ $(($cur+$step)) -gt $max ]; then
    setbrt $max
    exit 1
fi
setbrt $(($cur+$step))